Cytogenetic Analysis On Wheat-rye Hybrids

Common wheat line D-2-3-4 has high crossability with rye and the resultant F1 plants have a low fertility. During the selfing process of hybrids, rye chromosomes will rapidly loss and finally form cytotypes with 42 or 44 chromosomes. In order to clarify the reasons for these and evaluate the applying value of D-2-3-4 in distant hybridization, we analyzed the cytological behaviors of its F1, F2, and F3 hybrids with rye.1. During meiotic metaphase I of pollen mother cells (PMCs) in F1 hybrids, most chromosomes were existed as univalents but a few as bivalents or multivalents, with an average pairing configuration of 22.79 Ⅰ+2.38 Ⅱ (rod)+0.14 Ⅱ (ring)+0.05 Ⅲ. GISH revealed that chromosome pairing mostly took place in wheat-wheat chromosomes. However, a few chromosome pairing occurred in wheat-rye, indicating the utility value of D-2-3-4 in inducing wheat-rye homeologous pairing. The low fertility of D-2-3-4/rye hybrids was probably attributed to the observed phenomenon that sister chromatids separate during its meiotic anaphase Ⅰ.2. Among the analyzed seven F2 plants, six had 49 and one had 46 chromosomes in root-tip cells. However, the chromosome number of their F3 ranged from 42 to 47, demonstrating chromosome loss happened from F2 to F3. GISH analysis displayed that the average chromosome number of F2 and F3 were 41.57 wheat chromosomes with 6.57 rye chromosomes and 40.50 wheat chromosomes with 2.44 rye chromosomes, respectively. This indicated that the chromosome loss mainly took place in rye chromosomes. This loss did not occur in mitotic process. But, sister chromatids separate mainly for rye univalents was observed during meiotic anaphase Ⅰ of F2 plants, which may be responsible for the quick loss of rye chromsomes.3. Among the analyzed five F2 plants by multicolor in situ hybridization, two had the chromosome constitution of 42W+(1R-7R) and the remaining three respectively was 42W +(1R, Ⅱ2R,4R,5R, Ⅱ 6R),41W+ (2R,4R,5R,7R)+ 1RS/1BL, and 41W+(1R-7R)+ 1RS/1BL. We speculated, therefore, the chromosome number in their progenies might restore to 42 (such as substitution) or 44 (addition line); It seems that the production of 1RS/1BL translocation was not an accident event.4. We found the translocation existence with a small rye fragment in the hybrid progenies of D-2-3-4 with rye, thus indicate that D-2-3-4 may be used for developing translocation line.In conclusion, the high crossability between D-2-3-4 and rye and middle-level of homoeologous pairing similar with the role of ph2 gene in their F1 hybrids indicated the utility value in alien gene transfer by distant hybrids. Again, this value was enhanced by the sister chromatids separate during meiotic anaphase I in both Fi and F2 that is useful for the quick production of translocation, substitution, and addition lines.